Fire alarm devices such as audible horns (audible/visible or A/V), loudspeakers (speaker/visible or S/V) and visible strobes (visible only or V/O), are referred to as “notification appliances.” Typically, a fire alarm control panel (FACP) drives these devices over one or more “notification appliance circuits” (NACs). The strobes are used, for example, as an alert for the hearing-impaired, or for those in a high noise environment.
One type of strobe uses a flash tube (also called a flash lamp). Typically, the flash tube is an electric glow discharge lamp designed to produce extremely intense, incoherent, full-spectrum white light for very short durations. Flash tubes are made of a length of glass tubing with electrodes at either end and are filled with a gas that, when triggered, ionizes and conducts a high voltage pulse to produce the light. Xenon is an example of the gas that can fill the flash tube, with a Xenon flash tube producing a high-intensity light (such as hundreds of thousands of lumens) for a very short duration pulse (such as hundreds of milliseconds). Xenon flash tubes use a high voltage storage element, such as an electrolytic capacitor, that can be charged several hundred volts to provide energy for the flash. Xenon flash tubes also use a trigger voltage that is in the several thousand volt range to start the gas discharge.
The lifetime of the flash tube can depend on both the energy level used for the lamp in proportion to its discharge energy, and on the pulse duration of the lamp. Failures can be catastrophic or can be gradual, reducing the performance of the lamp below a usable rating.
Another type of strobe is Light Emitting Diode (LED)-based. An LED-based strobe cannot generate light at as high of an intensity as a Xenon-based strobe. Instead, LED-based strobes generate a lower intensity light (such as hundreds of lumens) for a longer period of time (such as tens to hundreds of milliseconds). In this way, the LED-based strobes can generate a comparable amount of light energy, as measured in candela, as a Xenon-based strobe. Further, an LED-based strobe is a semiconductor device that can be run off a lower voltage than a Xenon-based strobe, thus eliminating the high voltage circuitry. A capacitor may still be used for energy storage in the LED-based strobe, albeit for a lower output voltage. Because of its physical characteristics, an LED-based strobe can be turned on either continuously or pulsed. Factors that may limit the light output of the LED-based strobe are junction temperature and luminosity versus current, as determined by the LED chip materials and bonding wires. Finally, in contrast to flash-tube based strobes, LED-based strobes typically have a longer usable lifetime. However, LED-based strobes still lack the extremely intense light output generated by a flash tube based strobe.